The Thermal Abundance of Semi-Relativistic Relics - High Energy Physics - PhenomenologyReport as inadecuate




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Abstract: Approximate analytical solutions of the Boltzmann equation for particles thatare either extremely relativistic or non-relativistic when they decouple fromthe thermal bath are well established. However, no analytical formula for therelic density of particles that are semi-relativistic at decoupling is yetknown. We propose a new ansatz for the thermal average of the annihilationcross sections for such particles, and find a semi-analytical treatment forcalculating their relic densities. As examples, we consider Majorana- andDirac-type neutrinos. We show that such semi-relativistic relics cannot be goodcold Dark Matter candidates. However, late decays of meta-stablesemi-relativistic relics might have released a large amount of entropy, therebydiluting the density of other, unwanted relics.



Author: Manuel Drees, Mitsuru Kakizaki, Suchita Kulkarni

Source: https://arxiv.org/







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